A Global Perspective of Atmospheric CO2 Concentrations
William M Putman, Lesley Ott, Anton Darmenov and Arlindo daSilva
Global Modeling and Assimilation Office, NASA/Goddard Space Flight Center
Carbon dioxide (CO2) is the most important greenhouse gas affected by human activity. About
half of the CO2 emitted from fossil fuel combustion remains in the atmosphere, contributing to
rising temperatures, while the other half is absorbed by natural land and ocean carbon reservoirs.
Despite the importance of CO2, many questions remain regarding the processes that control these
fluxes and how they may change in response to a changing climate. The Orbiting Carbon
Observatory-2 (OCO-2), launched on July 2, 2014, is NASA's first satellite mission designed to
provide the global view of atmospheric CO2 needed to better understand both human emissions
and natural fluxes. This visualization shows how column CO2 mixing ratio, the quantity
observed by OCO-2, varies throughout the year. By observing spatial and temporal gradients in
CO2 like those shown, OCO-2 data will improve our understanding of carbon flux estimates.
But, CO2 observations can't do that alone. This visualization also shows that column CO2 mixing
ratios are strongly affected by large-scale weather systems. In order to fully understand carbon
flux processes, OCO-2 observations and atmospheric models will work closely together to
determine when and where observed CO2 came from. Together, the combination of highresolution data and models will guide climate models towards more reliable predictions of future
conditions.
The CO2 concentrations seen in this visualization are produced by a high-resolution (7-km) nonhydrostatic global mesoscale simulation using the Goddard Earth Observing System (GEOS-5)
model. This 7-km GEOS-5 Nature Run (7km-G5NR) product will provide synthetic observations
for observing systems like OCO-2. While global models like GEOS-5 are regularly applied in
seasonal-to-decadal climate simulations at much coarser resolutions, GEOS-5 is also uniquely
adaptable for application as a global mesoscale model in pursuit of global cloud resolving
applications at horizontal resolutions much finer than the highest resolution weather models used
around the world. Recent computing advances have permitted experimentation with global
atmospheric models at these scales, although production applications like the 7km-G5NR have
remained limited. Utilizing 480 2.8 GHz 16-core Xeon Sandy Bridge nodes of the NASA Center
for Climate Simulation (NCCS) “Discover” cluster, the 7km-G5NR produced over 2-years of
high-resolution weather and chemistry data at 30-minute intervals for the period May-2005 to
June-2007. The output from this massive computation totaled nearly 4 Petabytes and was
produced in a remarkable time of just over 75-days of dedicated computation on the Discover
cluster. More than 20 Terabytes of data are used to produce this visualization in a parallel image
processing mode using 128 ENVI/IDL processes (Exelis Visual Information
Solutions/Interactive Data Language, Boulder, Colorado) on the NCCS data analysis cluster
“Dali”. Simulations like the 7km-G5NR and these visualizations provide a valuable resource to
assist weather/climate scientists in determining how new observations from space can help us
improve our understating and predictability of weather and climate around the globe.
The visualization
This visualization compresses nearly 2 years of data into a few short minutes. It begins with a
global view of clouds and aerosols as seen from space on a satellite projection of the Earth. High
resolution ‘blue marble’ images from the Moderate Resolution Imaging Spectroradiometer
(MODIS) aboard the Terra (EOS AM) and Aqua (EOS PM) satellites and ‘black marble’ images
from the Visible Infrared Imaging Radiometer Suite on the Suomi National Polar-orbiting
Partnership (Suomi NPP) satellite provide the backdrop for our model data on the surface of the
globe.
As the satellite projection shifts to a full Cartesian view, global clouds highlight complex
weather systems across the world while dust, organic/black carbon, and sulfate aerosols are
transported within the prevailing circulation of the global weather. Clouds play a critical role in
the Earth’s weather/climate system. With horizontal resolution increased to 7-km, GEOS-5 now
resolves clusters of clouds rather than simply relying on the statistical effects of cloud systems
over large grid boxes. Simulated cloud clusters within the ITCZ, tropical storms, and midlatitude storms begin to resemble clouds as observed from space.
Aerosols have a significant effect on both weather and climate. They are transported around the
globe far from their source regions, interacting with weather systems, scattering and absorbing
solar and terrestrial radiation, and modifying cloud micro- and macro-physical properties. They
are recognized as one of the most important forcing agents in the climate system (Forster et al.
2007). Several missions in the Decadal Survey portfolio (e.g., ACE, Geo-CAPE), as well as the
Cloud-Aerosol Transport System (CATS) mission, that will fly on the International Space
Station (ISS), aim to get new information on aerosol distributions and properties.
Sulfur dioxide (SO2), produced during the burning of fossil fuels and from volcanic eruptions, is
a short lived gas which can act as pollutant near the surface with detrimental health and
acidifying effects. With a mean lifetime of just a couple of days in the troposphere, emitted SO2
is quickly converted to sulfate aerosol (SO4) through oxidation by OH or by reaction with H2O2
within clouds. The resulting SO4 exerts a direct radiative effect on the atmosphere and it can also
have an indirect radiative effect by inducing changes in cloud and precipitation microphysics.
The October 2005 eruption of the Sierra Negra Volcano on Isabella Island in the Galapagos
Islands produces a large plume of sulfate aerosols, as seen being dispersed in the 7-km GEOS-5
Nature Run from October 25th into early November 2005.
Carbon exists in many forms e.g., CO2, carbon monoxide (CO) and continually cycles through
Earth's atmosphere, ocean, and terrestrial ecosystems. This visualization shifts to column
concentrations of atmospheric CO2 (colored shades) and CO (white shades underneath) from
January 1, 2006 to December 31, 2006. CO2 variations are largely controlled by fossil fuel
emissions and seasonal fluxes of carbon between the atmosphere and land biosphere. CO2
concentrations are enhanced by carbon sources, mainly from human activities. During Northern
Hemisphere spring and summer months, plants absorb a substantial amount of CO2 through
photosynthesis, thus removing CO2 from the atmosphere. Atmospheric CO, a pollutant harmful
to human health, is produced mainly from fossil fuel combustion and biomass burning. Here,
high concentrations of CO (white) are mainly from fire activity in Africa, South America, and
Australia.
Due to the steady increase in global CO2 concentrations, visualizing multiple years of data
presents a unique challenge for representing this dynamic gas. The annual drawdown of CO2 by
plants in northern hemisphere summer months is clearly evident in this visualization. During
these summer months, plumes of CO emissions stream from biomass burning in boreal forests
across Canada and Siberia, while fires throughout Africa, Australia and southeast Asia continue
to produce large amounts of CO and CO2. The growth in CO2 concentration throughout the
simulation becomes clear as we move into 2007 where northern hemisphere CO2 concentrations
reach in excess of 395 ppmv and is highlighted by sampling the CO2 concentration from the
simulation at Mauna Loa, Hawaii. This location is the longest on record for CO2 concentration
across the globe [Keeling et al, 1976 and Thoning et al 1989]. The growth of CO2 concentration
at Mauna Loa over these two years exceeds 4 ppmv in this GEOS-5 simulation. The variability
of CO2 across the northern hemisphere is striking. The highest concentrations are focused around
major emission sources over North America, Europe and Asia, and the dispersion of these
emissions are controlled by the large-scale weather patterns within the global circulation creating
sharp gradients of CO2 along frontal boundaries and swirling within large weather systems.
OCO-2 will be the first NASA satellite mission to provide a global view of atmospheric CO2 to
better understand both human emissions and natural fluxes. OCO-2 observations and
atmospheric models like GEOS-5 will work closely together to fully understand carbon flux
processes and help guide climate models toward more reliable predictions of future conditions.
The 7km-G5NR will provide synthetic observations for observing systems like OCO-2 as seen
during the first few months of 2007 in this visualization. While actual swath data from OCO-2
was not available at the time this visualization was completed, OCO-2 is part of the A-Train
constellation of satellites and a generic polar orbiting swath was used to sample the 7km-G5NR
for this visualization.
The GEOS-5 Model
High-resolution global atmospheric models provide a unique tool to study the role of weather
within the global climate system. NASA supercomputing resources facilitate the development of
high-performance global modeling with the GEOS-5 model [Rienecker et al, 2008] at the highest
resolutions run to date for any global model [Putman and Suarez, 2011]. These global mesoscale
simulations with GEOS-5 represent multiple scales of atmospheric events from clusters of deep
convection and mesoscale convective complexes, to hurricanes, to large mid-latitude storm
systems, all within a cohesive simulation of the global circulation.
The finite-volume (FV) dynamics utilized within GEOS-5 evolved from the original FV
algorithm of Lin (2004), it has been extended to operate in a general curvilinear coordinate
system on the cubed-sphere grid [Putman and Lin (2007) and Putman and Lin (2009)]. The
hydrostatic formulation of Lin (2004) has been extended to the fully compressible nonhydrostatic flow (essentially the un-approximated Euler equations on the sphere). To maintain
the advantages of the “vertically Lagrangian discretization” of the hydrostatic system, an explicit
sound wave solver based on the conservation of Riemann invariants was developed.
The GEOS-5 AGCM physics includes parameterization schemes for atmospheric convection,
large-scale precipitation and cloud cover, longwave and shortwave radiation, turbulence, gravity
wave drag, a land surface model, and a simple glacier model. These physics parameterizations
are scale aware and dynamically adapt to the horizontal resolution of GEOS-5. This multi-scale
design allows GEOS-5 to easily move from climate simulations on the order of 50- to 100-km
resolutions, to cloud permitting resolutions of 7- to 3.5-km.
A version of the Goddard Chemistry, Aerosol, Radiation, and Transport model (GOCART,
Chin et al. 2002) run online and radiatively coupled in GEOS-5 as first described in Colarco et
al. (2010). GOCART treats the sources, sinks, and chemistry of dust, sulfate, sea salt, and black
and organic carbon aerosols. Both dust and sea-salt have wind-speed dependent emission
functions, while sulfate and carbonaceous species have emissions principally from fossil
fuel combustion, biomass burning, and biofuel consumption, with additional biogenic sources of
organic carbon. Sulfate has additional chemical production from oxidation of SO2 and DMS, and
we include a database of volcanic SO2 emissions and injection heights.
In addition to aerosol species, GEOS-5 simulates the emission and transport of CO and CO2. CO
is emitted from biomass burning, fossil and bio-fuel combustion, and produced chemically from
biogenic hydrocarbon and methane oxidation; the CO chemistry used in the 7km-G5NR is
described in Ott et al. (2010). CO2 is also emitted by fossil fuel combustion and biomass burning.
Natural fluxes of CO2 between the atmosphere and land and ocean carbon reservoirs, calculated
as part of NASA’s Carbon Monitoring System (CMS) Flux Pilot Project (Ott et al., 2014, in
review), are included.
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